The present invention relates to a clamping construction, and, more particularly, relates to a clamping construction adapted for clamping together two members in any one of a range of relative positions, which is easily adjusted and then clamped up initially, but which thereafter is difficult but not impossible to readjust with regard to the mutual fixing positions of the two members, thus inhibiting tampering while not preventing necessary repositioning.
The clamping construction according to the present invention is suitable for application to a wide range of circumstances in which it is required to clamp together two members in any one of a range of relative positions in such a way that their relative position can with some difficulty be adjusted later, but the particular inspiration for the present invention has come from the problem of finding a way to clamp an internal combustion engine distributor to the body of the internal combustion engine, i.e. to fix the rotational position of the distributor around the central axis thereof with respect to the internal combustion engine; and, accordingly, the clamping construction according to the present invention will be explained in terms of the fixing of the angular position of a distributor, although the clamping construction according to the present invention is capable of much more general application to a wide variety of circumstances and machines.
Generally, the distributor of an internal combustion engine is constructed with a body which is generally of a form substantially cylindrically symmetrical about the central rotational axis of the distributor shaft thereof. The distributor shaft conventionally bears at its end a rotary contact member such as a rotor arm, which distributes high tension electricity produced by the distributor to the various sparking plugs of the internal combustion engine, and which also bears at an intermediate point along its length a contact breaker points actuation cam, various seal washers and/or oiling washers, etc.. When the contact breaker actuation cam advances past a certain rotational angle with respect to the body of the distributor, then the distributor provides a sudden alteration of the electric current passing through a coil of the internal combustion engine, and this coil then produces a high tension electrical pulse which is transmitted to a particular one of the spark plugs of the engine, to spark said particular spark plug. Accordingly, since the central shaft of the distributor is rotationally coupled to the crankshaft of the internal combustion engine, and thus its rotational position is fixedly determined with respect to the rotational position of the crankshaft of the internal combustion engine, therefore the point in the crank angle diagram at which the spark is produced is determined by the rotational fixing position of the distributor body to the body of the internal combustion engine. In other words, in order to obtain a desired ignition timing, it is required to fix the distributor body positively with respect to the internal combustion engine at a prescribed fixing angle.
A general form of prior art construction has been for the lower part of the distributor, close to the central shaft thereof which protrudes into the engine so as to be rotationally coupled with the camshaft or the like thereof, to be formed as a tapered conical point which is closely engaged into a corresponding tapered conical hole formed in the body of the internal combustion engine. Accordingly, the distributor body has been fixed with respect to the internal combustion engine, except that said distributor body may be rotated around the central axis of the distributor shaft thereof. Further, there has been constructed a flange member projecting from the side of the distributor body sideways in a plane perpendicular to the central axis of the distributor. This flange member has been pierced with an elongated slot which has extended in an arc shaped form around a center which is the point on said central axis of the distributor where said central axis is intersected by said plane. This elongated slot has been in close proximity to a part of the outer wall of the internal combustion engine, and in this part of the outer wall of the internal combustion engine there has been formed a bolt hole with a female screw thread formed on the inner circumferential defining wall thereof. A bolt has been passed through this elongated slot, with the head of said bolt on the side of the flange member remote from the wall of the internal combustion engine, and with a male screw thread on the shank portion of said bolt engaged with the aforesaid bolt hole. In a variation of this prior art construction, the bolt has been engaged, not directly with the internal combustion engine outer wall, but with a fixing member which has been fixed to the internal combustion engine outer wall.
According to such a construction, when the bolt is somewhat slackened with respect to the member into which it is fixed, then the distributor may be rotated around its central axis fairly freely, the aforesaid conical tapering portion formed on the distributor body around the central shaft thereof sliding fairly freely in the aforesaid conical tapered hole formed in the body of the internal combustion engine; and at this time the head of the bolt slides along the side of the flange member remote from the wall of the internal combustion engine, and does not tightly grip the flange member. Accordingly, the distributor may be rotated so far in the one rotational direction and in the other for the bolt to reach the respective extreme ends of the circumferential slot in the flange member.
On the other hand, when it is desired to clamp the fixing angle of the distributor with respect to the body of the internal combustion engine, so as to fix the ignition timing of the internal combustion engine, then it is only necessary to tighten up the bolt, driving it into the member such as the wall of the internal combustion engine to which it is threaded, and when this is done the head of the bolt, possibly via an intermediate washer, bears tightly on the side of the flange member remote from the wall of the internal combustion engine, and presses the flange member generally against the wall of the internal combustion engine. Thus, by the friction between the flange member and the head of the bolt or the washer interposed therebetween, and also by the friction of the flange member directly against the member such as the wall of the internal combustion engine to which the bolt is fitted, and against which said flange member is pressed by the tension of the bolt, the distributor is positively prevented from rotating about its central axis, thus fixing the ignition timing of the internal combustion engine.
However, a disadvantage of this prior art construction is that it is too easy to adjust. In more detail, it is of course essential for the fixing angle of the distributor with respect to the wall of the internal combustion engine to be adjustable at the factory, when the internal combustion engine is being assembled, in order for an appropriate ignition timing for the engine to be set, because it is impossible to manufacture the parts of the internal combustion engine and of the distributor so accurately as to dispense with initial adjustment of the ignition timing. Thus, initially, adjustability of the fixing angle of the distributor with respect to the internal combustion engine must be easy, simple, and sure. On the other hand, once the vehicle has been passed out from the factory and has been sold to a user, it is not desirable that it should be very easy to change the fixing angle of the distributor with respect to the internal combustion engine, and thus to alter the ignition timing.
This is because there are many vehicle users who are inclined to tamper with the timing of the internal combustion engine, by altering the fixing angle of the distributor with respect to the wall thereof, either under a mistaken impression that by doing so they are setting the ignition timing back to the true or correct ignition timing, or through a surreptitious desire to alter the performance characteristics of the internal combustion engine, such as for instance in order to generate more power therefrom, or in order to fit unauthorized ignition modifications. In this case, there is a strong possibility that this alteration of the ignition timing of the internal combustion engine by altering the fixing angle of the distributor to the side wall thereof may cause the density of harmful components in the exhaust gases emitted by the internal combustion engine to be increased. This is because of the sensitivity of various systems for controlling the density of harmful components in the exhaust gases of an internal combustion engine to the ignition timing of that internal combustion engine, and is becoming more and more a fact of the automobile art nowadays.
Thus, it is desirable that it should be quite difficult to change the fixing angle of the distributor with respect to the outer wall of the internal combustion engine, once the vehicle has been delivered from the factory. The above outlined form of construction for fixing the angle of the distributor with respect to the outer wall of the internal combustion engine fails to meet this criterion; in fact, at all times, it is very easy to alter the fixing angle of the distributor with respect to the outer wall of the engine, and thereby to alter the ignition timing; this can be done easily, both initially at the factory, later by an unauthorized mechanic working on the internal combustion engine, and also by an authorized workplace which is performing authorized service operations. In this connection, it should be noted that, even after the vehicle has been delivered from the factory, it is required that it should be possible, although preferably not very easy, for the fixing angle of the distributor with respect to the outer wall of the engine, and thereby the ignition timing, to be altered. This is because the characteristics of various of the parts of the distributor and of the internal combustion engine, such as the profile of the ignition cam thereof, and the state of wear of the ignition contact breaker points thereof, etc., may change over a long period of service use of the vehicle incorporating the engine. Accordingly, it is sometimes necessary for the fixing angle of the distributor with respect to the outer wall of the internal combustion engine to be altered, in order to maintain the same desired proper ignition timing as was set at the factory. This operation of setting the ignition timing can in principle be simply and easily performed by an appropriately equipped workplace by altering the fixing angle of the distributor with respect to the engine, and accordingly it is desirable that this alteration of the fixing angle of the distributor with respect to the outer wall of the internal combustion engine should be possible to be performed at an authorized workplace.
The above proposed construction for the fixing of the aforesaid flange member with respect to the outer wall of the internal combustion engine suffers from the defect that it is too easy to adjust. In other words, merely by slackening the fixing bolt, any person of even low mechanical skill can then twist the distributor with respect to the outer wall of the internal combustion engine, can thereby alter its fixing position with respect thereto, and accordingly can alter the ignition timing of the internal combustion engine. This is becoming more and more of a problem nowadays, with respect to the sensitivity of systems for removing harmful components from the exhaust gases of the engine, and it is very desirable that some means should be found for overcoming this problem of easy tampering.
A solution which has been proposed as a construction for fixing the fixing angle of a distributor with respect to the outer wall of an internal combustion engine has been for the aperture in the above described flange member to be formed not as an elongated slot, but on the contrary as a cylindrical bolt hole of approximately the same size as the aforesaid fixing bolt. Thus, when the bolt has been passed through the bolt hole in the aforesaid flange and has been screwed into the bolt hole in the fixing member such as the wall of the internal combustion engine, it is completely impossible for the fixing angle of the distributor with respect to the body of the internal combustion engine to be in any way altered. In this case, of course tampering is rendered quite impossible; but in fact it is impracticable under normal mass production conditions for the parts of the internal combustion engine and of the distributor thereof to be constructed so accurately and so free from the effects of manufacturing tolerances that the timing of the internal combustion engine can be accurately and properly preset in such a built in way. Accordingly, it becomes impossible to obtain proper ignition timing for such an internal combustion engine, and accordingly this solution is not practicable. In fact, even if it were possible initially to attain the correct ignition timing for such an internal combustion engine at the factory, then, according to this construction, even in an authorized workplace such as a garage it would be impossible to adjust the fixing angle of the distributor with respect to the wall of the internal combustion engine, in order to compensate for slight changes in the parts of the distributor and of the internal combustion engine, so as to return the ignition timing of the internal combustion engine to the proper ignition timing, after the ignition timing setting has wandered slightly from the proper ignition timing setting. Thus, in summary, this has proved to be not a practicable solution to the problem of tampering.